There are many situations where is it desirable to locate buried utilities such as pipes and cables. For example, before starting any new construction that involves excavation, worker safety and project economic concerns require the location and identification of existing underground utilities such as underground power lines, gas lines, phone lines, fiber optic cable conduits, cable television (CATV) cables, sprinkler control wiring, water pipes, sewer pipes, etc., collectively and individually herein referred to as “buried objects.”
As used herein, the term “buried objects” also includes objects located inside walls, between floors in multi-story buildings or cast into concrete slabs, for example, as well as objects disposed below the surface of the ground. If excavation equipment such as a backhoe hits a high voltage line or a gas line, serious injury and property damage may result. Unintended severing of water mains and sewer lines generally leads to messy and expensive cleanup efforts. The unintended destruction of power and data cables may seriously disrupt the comfort and convenience of residents and bring huge financial costs to business. Accordingly, the art is replete with proposed solutions to the buried object locating problem, including a number of patents and patent applications owned by SeekTech, Inc., assignee of the instant application.
A sonde typically includes a coil of wire wrapped around a ferromagnetic core that is packaged for insertion into a buried nonconductive conduit, such as a plastic utility runway or a concrete water pipe to generate electromagnetic energy. Still other buried objects, such as conductive lines and pipes, may be located by first applying an external signal to the object to induce a current flow therein, thereby generating a magnetic field that may be detected by a magnetic sensor. In some applications, currents may be induced into the buried object by existing magnetic fields, such as those sent from commercial or military radio transmitters or other transmitting devices.
In an exemplary buried object locating system, an external electrical signal source (also known as a buried object transmitter or just “transmitter” for brevity) having a frequency in the range of approximately 4 Hz to 500 kHz has a well-known utility for energizing conductive objects by direct electrical coupling to permit their location through sensing of emitted magnetic fields. Other buried objects, such as underground power transmission lines, inherently carry current which generates surrounding magnetic fields. These examples of active and passive locating of buried conductors are also commonly described as “line tracing.”